1. Field of Invention
The present invention relates generally to rotating head assemblies of apparatus for applying a liquid photoresist solution to a semiconductor wafer, and more particularly to rotating head assemblies of mounting a semiconductor wafer for applying a liquid photoresist solution thereto.
2. The State of Art
The processing of a semiconductor wafer to produce integrated circuit structures generally involves a series of steps in the course of which a layer of a liquid photoresist solution is formed covering the wafer surface.
Following the photoresist application step, on the coated surface of the wafer, a photomask plate is placed to form a pattern of a desired circuit. For the above purpose, the wafer must be coated by a uniform photoresist film or layer.
In the prior art, the application of the liquid photoresist solution to the surface of the wafer is carried out by using rotating apparatus to be referred to as a "spincoater". The wafer is mounted on a rotating disk of the spincoater, and is secured to the disk by suction of air by means of a vacuum pump, and the disk is rotated at the high speed in dropping the liquid photoresist solution on the surface of the wafer.
A coated film of the photoresist formed in the above manner, however, tends to increase in thickness at the periphery of each corner of a rectangular wafer by the action of centrifugal force, and a portion of the solution to be applied to the surface of the wafer is splashed from the wafer in the air.
According to the prior art, it is very difficult to align the center of the wafer into the axis of rotation of the disk.